High temperature ceramics (HTC) and ultrahigh temperature ceramics (UHTC) are ceramic materials that typically have melting points above 2500-3000° C. HTC and UHTC, in the form of powders, monolithic ceramics, or composites, find many important applications from grinding and cutting materials in machinery and mining industries to thermal insulation tiles, missile nozzles, and hypersonic vehicle leading edges in the aerospace industry. Reducing the size of HTC and UHTC powders from microns to submicrons and even into the nanometer range (i.e., <˜100 nm) offers additional benefits, such as simplified post-synthesis powder processing. Benefits of simplified post-synthesis powder processing include reducing the need for extensive grinding, lowering the sintering temperature and associated energy consumption for materials processing and densification, and greater ease in manufacturing products with sub-micron or even nano-sized grains. These advantages often lead to improved mechanical properties such as strength, hardness, and toughness of the ceramic materials. In addition, nanopowders offer flexibility in subsequent processing techniques to make either bulk ceramics via powder consolidation or coatings via techniques such as plasma spray.
Although synthesis of nano-sized HTC and UHTC powders has been studied for some time, most methods suffer from drawbacks in terms of cost, product quality, and process safety. For example, nano-TaC has been synthesized using an RF plasma method in a quick one step process, but the method uses costly organometallic precursors and hydrogen gas and several steps in the operation have to be carried out in a glove-box. Similarly, combustion synthesis or self-propagating high-temperature synthesis (SHS) methods are fast, but suffer from limitations related to the nature of batch processing and difficulty in process control due to too short reaction times for SHS. In addition, mechanical milling is often involved for SHS, which also raises contamination concerns. Therefore, there is a continued need for new methods and apparatuses for producing high temperature ceramics.